Ryan Reynolds is set to run the New York City Marathon on November 2 in aid of his father Jim, who suffers from Parkinson's Disease

Ryan Reynolds is set to run the New York City Marathon for his father.

The 'Definitely, Maybe' star - who married Scarlett Johansson in an intimate ceremony last month in Canada - will be raising money for Parkinson's Disease through the event on November 2, in a tribute to his father Jim.

In an open letter printed in The Huffington Post newspaper, Ryan wrote: "I am not a runner. I am a running joke. Waking up at 4.30am and jogging anywhere from 11 to 23 miles has been nothing short of horrifying.

"But this is on behalf of my father, Jim Reynolds, who has spent the last 15 years in a life or death struggle with Parkinson's Disease."

Ryan, 31, also revealed he has been finding it tough training for the 26-mile race.

He added: "Not since the discovery of junior high school has a torture been so effective. It's my hope the story of my father, combined with my own goal of becoming the first person in history to sob uncontrollably for 26.2 miles straight, may inspire you to give something too."

Parkinson's Disease is a disorder of the central nervous system which affects the sufferer's speech, motor skills and other functions.